The invention relates to managing power states in a computer system.
In a continuing effort to reduce the amount of power consumed by computer systems, various power management solutions exist. For example, a computer system can be placed into a low power state in response to a predetermined period of inactivity. Thus, if peripheral devices on a computer system have been inactive for the predetermined period, a system management interrupt is generated to invoke a handler that places components in the system in reduced power consumption states (such as shutting off clocks to components, removing power from components, blanking the video display, or spinning down the hard drive).
The Advanced Power Management (APM) Standard (Revision 1.2) defines several levels of power states having different levels of power consumption. The APM standard defines the following power states in decreasing order of power consumption: Full On (no power management); APM Enabled (system is on but unused devices may not be powered); APM Standby (one reduced level of power consumption); APM Suspend (another reduced level of power consumption), and Off (system is not working and power supply is off). In the Standby state, the CPU clock is slowed or stopped, and many devices are placed in a lower power mode; however, most operational parameters are retained so that recovery from the APM Standby state can appear almost instantaneous to the user. In the Suspend state, the system is in a state of greater power savings, in which power can be cut off from most power managed devices, the CPU clock is stopped, the CPU core is in its minimum power state, and clock is stopped (which causes system bus devices to be disabled).
By disabling many of the devices in the system in the APM Suspend mode, a device may be unable to respond to an external event received at an input port of the computer system, or alternatively, the device may receive the event but may be unable to notify the rest of the system of the event (such as by interrupt). As a result, some external events may be missed by the computer system when it is in a low power mode such as the APM Suspend state.
Generally, the invention is directed to switching to a second low power state even though a first low power state has been requested in a computer system.
The invention may have one or more of the following advantages. By switching the computer system to the second power state rather than the first power state (in which the first power state can be a more reduced power consumption state than the second power state), certain devices can remain enabled so that they can respond to specified events and not miss those events. Power savings can thus be achieved while still maintaining responsiveness of the computer system to specified events.
In general, in one aspect, the invention features a computer system having first and second low power states. The computer system includes a processor, a controller configured to generate a request to transition to the first low power state, and a program executable by the processor and configured to respond to the request by causing the system to transition to the second low power state.
In general, in another aspect, the invention features a method of managing a computer""s power state, including generating a request to enter a first low power state. The request to enter the first low power state is denied, and in response to denying the request, a notification is issued to enter a second low prostate.
In general, in another aspect, the invention features a method that generates a request to switch power saving states of a computer from a first state to a second state. The request is acted on by instead switching to a third power state.
In general, in another aspect, the invention features a computer system having a processor, a first program executable by the processor to detect a predefined event and to generate a power savings request in response to detection of the event. A second program executable by the processor intercepts the request and denies the request.
In general, in another aspect, the invention features a computer-readable storage medium for use in a computer system having first and second low power states. The storage medium contains instructions for causing a computer system to generate a request to enter into the first low power state, to deny the request to enter the first low power state, and to issue a notification to enter the second low power state in response to the denying of the request.
Other features and advantages will become apparent from the following description and from the claims.